Hmm, at £450 you're sort of on the verge of (what could be described as) good amp territory...
My theory on amps is that you should buy one that will last you a good few years...I started off looking at the 100 watt Vox Valvetronix amp, thinking that it would be sound for gigging with for now and that I can upgrade in a year or so.
However, then I decided that if I buy an amp now, and then in a year buy a new one, I wouldn't be able to afford anything near as good as if I waited a few months and saved up my money, and bought a better amp now.
I would recommend you save for an Engl Screamer combo, as it should manage all the music you want to get fairly easily without pedals - the heaviest I've really gone on mine is Megadeth, but that's only on channel 3 (of 4) so there's plenty of scope to go heavier if needed...
You can find them (I believe) for about £650ish, even less than that if you look used - mine cost me £500 :drink: